A solid-state imaging device intended to be used for intraoral X-ray imaging has been disclosed in Patent Document 1. For such application, the incident period of X-rays to be imaged is considerably short, so that the solid-state imaging device must capture the timing of incidence of X-rays to image the X-rays. Therefore, the solid-state imaging device disclosed in Patent Document 1 includes not only an imaging photodetecting section where pixel units including photodiodes are two-dimensionally arrayed in order to take an X-ray image but also separately a trigger photodiode for detecting an incidence of X-rays. And, this solid-state imaging device detects an incidence of X-rays by monitoring an electrical signal output from the trigger photodiode and then obtains an X-ray image based on an electrical signal output from the imaging photodetecting section.
Moreover, solid-state imaging devices can be divided based on configuration into an APS (Active Pixel Sensor) type and a PPS (Passive Pixel Sensor) type. The solid-state imaging device disclosed in Patent Document 1 is of an APS type. A pixel unit in the case of an APS type includes a photodiode for generating charge of an amount according to an incident light amount, a floating diffusion region serving as a charge accumulating section for accumulating the charge, and an amplifying transistor having a gate electrode electrically connected with the floating diffusion region.
The APS type solid-state imaging device can, at the same timing in the plurality of pixel units of the photodetecting section, discharge a junction capacitance section of the photodiode and the floating diffusion region, generate charge in the photodiode, transfer the generated charge to the floating diffusion region, and accumulate the transferred charge in the floating diffusion region. Then, this solid-state imaging device can, in order row by row in the photodetecting section, output data according to an amount of charge accumulated in the floating diffusion region of each pixel unit from the amplifying transistor. This imaging operation is called a global shutter type.
In contrast thereto, in a rolling shutter type imaging operation, charge generation in the photodiode, charge accumulation, and data output are performed in order with a shift of the period row by row in the photodetecting section. In the rolling shutter type imaging operation, respective frames of image data obtained by imaging are data obtained at different times depending on the row.
In a global shutter type imaging operation, respective frames of image data obtained by imaging are data obtained at the same time regardless of the row. Therefore, when the incident period of light to be imaged is considerably short as in intraoral X-ray imaging, the global shutter type imaging operation is preferred.